Trait tokio_io::codec::Decoder
[−]
[src]
pub trait Decoder { type Item; type Error: From<Error>; fn decode(
&mut self,
src: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error>; fn decode_eof(
&mut self,
buf: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error> { ... } }
Decoding of frames via buffers.
This trait is used when constructing an instance of Framed
or
FramedRead
. An implementation of Decoder
takes a byte stream that has
already been buffered in src
and decodes the data into a stream of
Self::Item
frames.
Implementations are able to track state on self
, which enables
implementing stateful streaming parsers. In many cases, though, this type
will simply be a unit struct (e.g. struct HttpDecoder
).
Associated Types
type Item
The type of decoded frames.
type Error: From<Error>
The type of unrecoverable frame decoding errors.
If an individual message is ill-formed but can be ignored without
interfering with the processing of future messages, it may be more
useful to report the failure as an Item
.
From<io::Error>
is required in the interest of making Error
suitable
for returning directly from a FramedRead
, and to enable the default
implementation of decode_eof
to yield an io::Error
when the decoder
fails to consume all available data.
Note that implementors of this trait can simply indicate type Error = io::Error
to use I/O errors as this type.
Required Methods
fn decode(
&mut self,
src: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error>
&mut self,
src: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error>
Attempts to decode a frame from the provided buffer of bytes.
This method is called by FramedRead
whenever bytes are ready to be
parsed. The provided buffer of bytes is what's been read so far, and
this instance of Decode
can determine whether an entire frame is in
the buffer and is ready to be returned.
If an entire frame is available, then this instance will remove those bytes from the buffer provided and return them as a decoded frame. Note that removing bytes from the provided buffer doesn't always necessarily copy the bytes, so this should be an efficient operation in most circumstances.
If the bytes look valid, but a frame isn't fully available yet, then
Ok(None)
is returned. This indicates to the Framed
instance that
it needs to read some more bytes before calling this method again.
Note that the bytes provided may be empty. If a previous call to
decode
consumed all the bytes in the buffer then decode
will be
called again until it returns None
, indicating that more bytes need to
be read.
Finally, if the bytes in the buffer are malformed then an error is
returned indicating why. This informs Framed
that the stream is now
corrupt and should be terminated.
Provided Methods
fn decode_eof(
&mut self,
buf: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error>
&mut self,
buf: &mut BytesMut
) -> Result<Option<Self::Item>, Self::Error>
A default method available to be called when there are no more bytes available to be read from the underlying I/O.
This method defaults to calling decode
and returns an error if
Ok(None)
is returned while there is unconsumed data in buf
.
Typically this doesn't need to be implemented unless the framing
protocol differs near the end of the stream.
Note that the buf
argument may be empty. If a previous call to
decode_eof
consumed all the bytes in the buffer, decode_eof
will be
called again until it returns None
, indicating that there are no more
frames to yield. This behavior enables returning finalization frames
that may not be based on inbound data.
Implementors
impl Decoder for BytesCodec type Item = BytesMut; type Error = Error;
impl Decoder for LinesCodec type Item = String; type Error = Error;